1. Field of the Invention
The present invention relates to a toner for developing an electrostatic latent image in electrophotography, electrostatic recording and electrostatic printing, and to a developer, a developer container, a process cartridge, an image forming apparatus and an image forming method using the toner.
2. Discussion of the Background
Image formation by electrophotography, electrostatic recording, electrostatic printing, etc. is typically performed by series of processes of forming an electrostatic latent image on an electrostatic latent image bearer (hereinafter referred to as a “photoreceptor” or an “electrophotographic photoreceptor”), developing the electrostatic latent image with a developer to form a visual (toner) image, transferring the visual image onto a recording medium such as papers and fixing the visual image thereon.
The developer includes a one-component developer using only a magnetic toner or a non-magnetic toner and a two-component developer including a toner and a carrier.
As a fixing method used in electrophotography, a heat roller method of directly contacting a heat roller to a toner image on a recording medium upon application of pressure to fix the toner image thereon is typically and widely used in terms of good energy efficiency. The heat roller method needs a large amount of electric power to fix a toner image. Therefore, various methods of reducing power consumption of the heat roller in terms of saving energy. For example, methods of decreasing a heater power for the heat roller when nor producing images and increasing the heat power to rise a temperature thereof when producing images are typically used.
However, about 10 sec standby time is needed to increase a temperature of the heat roller to fix a toner image from a time of sleep, which is a stress for a user. In addition, it is desired that the heater is completely off to reduce power consumption when images are not produced. A fixable temperature of a toner needs decreasing to solve these.
A toner for use in the developer is required to have good low-temperature fixability and storage stability (anti-blocking) with the development of electrophotography, and polyester resins having higher affinity with a recording medium and better low-temperature fixability than styrene resins having been conventionally and typically used as a binder resin for a toner are being more used. For example, Japanese published unexamined application No. 2004-254854 discloses a toner including a linear polyester resin the properties of which such as molecular weight are specified, and 4-70765 discloses a toner including a non-linear cross-linked polyester resin using rosins as an acidic component.
Conventional binder resins for a toner are insufficient to meet market's demands for an image forming apparatus having higher speed and saving more energy, and are very difficult to maintain sufficient fixing strength because fixing time of a fixer is shortened and heat temperature thereof lowers.
The toner including a polyester resin using rosins as disclosed in Japanese published unexamined application No. 4-70765 has good low-temperature fixability and pulverizability, and therefore has an advantage of improving productivity of a toner prepared by pulverization methods. As an alcohol component of the polyester resin, when 1,2-propanediol which is a branched-chain alcohol having 3 carbon atoms is used, the resultant toner has as good offset resistance as when an alcohol having 2 or less carbon atoms is used and has improved low-temperature fixability more than when the alcohol having 2 or less carbon atoms is used. In addition, 1,2-propanediol is more effective for preventing deterioration of storage stability due to lowering of glass transition temperature than a branched-chain alcohol having 4 carbon atoms or more. When such a polyester resin is used as a binder resin for a toner, the resultant toner has low-temperature fixability and improved storage stability.
However, demands for saving energy are more increasing from now, and although a polyester resin improves low-temperature fixability of a toner, in the near future, it is difficult only for the polyester resin to fully comply with the demands for saving energy.
Japanese published unexamined application No. 2006-208609 discloses a method of introducing a fixing supplemental component into a toner to improve low-temperature fixability thereof. Japanese published unexamined application No. 2006-208609 discloses a toner including a fixing supplemental component as a crystal domain to have both of thermostable storage stability and low-temperature fixability. A toner is required to have high durability and satisfy demands for saving more energy with speed up of image forming apparatus, however, a toner is difficult to fully comply with the demands at present and needs further improvement and development.
Because of these reasons, a need exists for a toner applicable in low-temperature fixing systems and being offset resistant.